1. Field of the Invention
The present invention relates to an optical disc drive apparatus suitable for applying to such an optical disc drive apparatus used for recording and/or reproducing audio/video data onto and/or from an optical disc such as a laser disc (LD) or a digital versatile disc (DVD), for example. More particularly, the present invention relates to an optical disc drive apparatus equipped with a skew servo mechanism which enables optical axis of optical beams emitted from an optical pickup unit to vertically follow up skew of a signal surface caused by the skewed disc surface.
2. Related Art
In a conventional optical disc drive apparatus, an optical disc such as a CD (Compact Disc), an LD (Laser Disc) or a DVD (Digital Versatile Disc) is mounted on a turn table linked with a spindle motor and rotated to cause optical beams emitted from an optical pickup unit to be focused on a signal surface of the optical disc. The optical pickup unit is guided by a pair of run guide shafts and is seeking in the radial direction of the optical disc and in the direction parallel to the signal surface of the optical disc, thereby recording and or reproducing operation of the optical disc is performed.
Nevertheless, inasmuch as an optical disc comprises a thin disc made of synthetic resin, while an optical disc mounted on a turn table is rotated, therefore the skew is easily generated on the optical disc. In particular, substantial skew is easily generated along an external periphery of the optical disc. Once such skew is generated on the optical disc rotated by the turn table, it causes a skew of the signal surface of the optical disc against the optical axis of the optical beams emitted from the optical pickup unit, and thereby it no longer possible to permit the optical beams focused via object lenses to be irradiated and to be reflected perpendicularly to the signal surface of the optical disc, thus degrading performance of the optical disc to properly record and/or reproduce audio/video data onto and/or from the optical disc.
In particular, in case of a high-density optical disc such as a digital versatile disc (DVD) for example, the wave length of the optical beams is shortened, numerical apertures (NA) of the objective lens are improved due to a high signal recording density in recent years. Because of this, even the slightest skew generated on the signal surface of an optical disc against optical axis of the object lenses causes deterioration of performance of the optical disc upon recording and/or reproducing audio/video data, thus generating a problem.
To deal with this problem, any of the conventional optical disc drive apparatuses incorporates such a skew servo mechanism which initially enables a skew sensor to detect a skew of the signal surface against the optical axis of the object lenses caused by the skew generated on the optical disc and then causes an optical pickup unit to follow up the signal surface of the optical disc in order that optical axis of the object lenses can become perpendicular to the signal surface on the back side of the optical disc.
Concretely, as shown in FIG. 21, according to a construction of any conventional skew servo mechanism, in order to enable an optical pickup unit 1 mounted with object lenses 1a to properly run itself in the X direction (i.e., radial direction) along a signal surface of an optical disc (not shown), a pair of parallel running guide shaft members 2 are secured to a first chassis 3 which is included in an aperture portion 4a formed on a second chassis 4. The first chassis 3 is rotatably and adjustably installed in the Z direction (i.e., vertical direction) against the signal surface of the optical disc by means of a horizontal pivot axis 5 which is orthogonal to a pair of the guide shaft members 2, where the above Z direction corresponds to the direction perpendicular to the second chassis 4. A spindle motor (not shown) linked with a turn table (not shown) is mounted on the second chassis 4. The second cassis 4 causes an elevating mechanism (not shown) to vertically drive the optical pickup unit 1 and the spindle motor into and out from a main chassis inside of a main body of the optical disc drive apparatus via rotating movement by way of pivoting on the horizontal pivot axis 5. Thereby chucking and un-chucking of the optical disc against the turn table of the spindle motor is done and simultaneously the object lens 1a of the optical pickup unit 1 is made to come close to and to depart from the signal surface on the back side of the optical disc. While executing the above processes, a skew sensor mounted on the optical pickup unit 1 detects a radial-directional skew along X direction against the signal surface of the optical disc while being rotated in the state chucked with the turn table connected to the spindle motor. Then, by executing angular adjustment of the first chassis 3 against the second chassis 4 by way of pivoting on the horizontal pivot axis 5 via a first chassis rotational adjustment mechanism (not shown) driven by a motor in the XZ direction (i.e., the vertical direction synthesized with the X direction and Y direction, the skew servo mechanism executes the skew servo controlling operation to cause the optical axis to follow up the signal surface of the optical disc in order that the optical axis of the object lenses 1a can become perpendicular to the signal surface on the back side of the optical disc. On the other hand, inasmuch as the above-cited conventional skew servo mechanism mounts the optical pickup unit 1 on the first chassis 3, and yet, since it is required to introduce a double-chassis system for adjusting a positional angle of the first chassis 3 relative to the positional angle of the second chassis 4. Thereby the number of component parts has been increased to result in the complication of a structure to further result in the increased weight and vibration to raise another problem. Further, it has been quite difficult to realize a high-speed seeking operation due to a variable space between the first and second chassis 3 and 4 via elapse of time, and yet, an actual skew servo controlling operation has failed to exert proper performance to full extent. Further, inasmuch as the above-cited conventional skew servo mechanism is capable of adjusting the rotation of the first chassis 3 solely in the XZ direction against the second chassis 4 by way of pivoting on the pivot axis 5 which is orthogonal to a pair of the guide shafts 2. Even though the above skew servo mechanism is capable of controlling a radial skew to enable the optical axis to follow up the signal surface of the optical disc in order that the optical axis of the object lens 1a can become perpendicular to the vertical directional skew on the signal surface of the optical disc, the above skew servo mechanism still fails to properly control a tangential skew for controlling the skew of the object lens 1a against the signal surface on the back of the optical disc in the tangential direction being orthogonal to radial direction generated in the course of executing such a process for controlling the focus servo-mechanism of the object lens 1a. 
The present invention has been achieved to fully solve the above problems by way of providing a novel optical disc drive apparatus which totally dispenses with introduction of the above-cited double-chassis system and makes it possible to execute bi-directional skew servo controlling operations in both the radial and tangential directions.
To achieve the above object, the optical disc drive apparatus realized by the present invention comprises: a pair of run guide shaft members disposed in parallel with each other, which jointly guide a skew servo mechanism by way of enabling an optical pickup unit to run itself in the radial direction along a signal surface of an optical disc, wherein the skew servo mechanism causes the optical pickup unit to follow up the signal surface in order that the optical axis of optical beams emitted from the optical pickup unit can become perpendicular to the signal surface of the optical disc; a pair of pivot members which are jointly secured to a chassis mounted with a spindle motor linked with a turn table, wherein said pivot members rotatably support an end of inner peripheral portions of an optical disc of the pair of run guide members in the direction perpendicular to the signal surface of the optical disc; a sliding cam which is slidably secured to a chassis and controls rotation of one end portions of a pair of run guide shaft members corresponding to an external peripheral side of the optical disc in the direction perpendicular to the signal surface of the optical disc by means of a pair of cam surfaces; a skew detecting means which detects a skew of the signal surface of the optical disc; and a slide cam driving means which controls a sliding movement of the above sliding cam based on the result detected by the above skew detecting means.
In the skew servo mechanism as described above, an actual skew generated on the signal surface of the optical disc is detected by the above skew detecting means to cause the above slide cam driving means to control the sliding movement of the above sliding cam. As a result, one end portions of a pair of run guide shaft members corresponding to the external peripheral side of the optical disc are driven by a pair of cam surfaces of the above slide cam to cause the pair of run guide shaft members to be rotatably controlled in the direction perpendicular to the signal surface of the optical disc by way of pivoting on a pair of pivot member supporting an end of the internal peripheral side of the optical disc. As a result, the skew servo controlling operation is executed by enabling the optical pickup unit to follow up the signal surface of the optical disc in order that optical axis of the optical beams emitted from the optical pickup unit running via guidance of the pair of run guide shaft members can become perpendicular to the signal surface of the optical disc. Inasmuch as the skew servo mechanism rotatably controls the pair of run guide shaft members for guiding the optical pickup unit, there is no need of introducing a double-chassis system, but the chassis mounted with a spindle motor is merely loaded with the inventive skew servo mechanism, whereby completing a single chassis construction.